Vacuum deposition and curing of liquid monomers apparatus

ABSTRACT

The present invention is the formation of solid polymer layers under vacuum. More specifically, the present invention is the use of &#34;standard&#34; polymer layer-making equipment that is generally used in an atmospheric environment in a vacuum, and degassing the monomer material prior to injection into the vacuum. Additional layers of polymer or metal or oxide may be vacuum deposited onto solid polymer layers. Formation of polymer layers under a vacuum improves material and surface characteristics, and subsequent quality of bonding to additional layers. Further advantages include use of less to no photoinitiator for curing, faster curing, fewer impurities in the polymer electrolyte, as well as improvement in material properties including no trapped gas resulting in greater density, and reduced monomer wetting angle that facilitates spreading of the monomer and provides a smoother finished surface.

This invention was made with Government support under ContactDE-AC06-76RLO 1830 awarded by the U.S. Department of Energy. TheGovernment has certain rights in the invention.

This patent application is a division of application Ser. No.08/100,883, filed Aug. 02, 1993, now U.S. Pat. No. 5,395,644 which is acontinuation-in-part of patent application Ser. No. 07/933,447, filedAug. 21, 1994, now Pat. No. 5,260,095, issued Nov. 03, 1993.

FIELD OF THE INVENTION

The present invention relates generally to a method of makingmulti-layer laminate structures from polymers and metals and/or oxides.More specifically, the present invention relates to forming solidpolymer laminate layers under vacuum. Additional layers of polymer ormetal or oxide may be added under vacuum as well.

BACKGROUND OF THE INVENTION

Laminate structures are used in many applications including but notlimited to electronic devices, packaging material, and solar reflectors.Laminate structures in electronic devices are found in devices includingbut not limited to circuit elements and electrochromic devices whereinconductive polymer layers are combined and may include a metal layerand/or an oxide layer. Electro- chromic devices include but are notlimited to switchable mirrors and switchable windows. Circuit elementsinclude active elements, for example fuel cells and batteries, andpassive elements, for example capacitors.

Presently, many laminate structures are made with solid polymer laminatelayers. In packaging material and solar reflectors, a metal layer may beadded to enhance optical reflectance. In electronic devices, a metallayer may be added to enhance electrical conductivity. In pack- agingmaterial and solar reflectors, it is not necessary that the polymerlayer or layers be conductive, whereas in electronic devices, especiallybatteries, the polymer layers must be conductive to act as electrolytes,anodes, and cathodes. Certain polymers when doped with selected saltsare known to make suitable solid polymer ion conduc- tive layers.Polymers known to be useful include but are not limited topolyethyleneoxide, polypropyleneoxide, polyorgansulfides, andpolyanaline. Suitable salts include but are not limited to lithiumsalts, for example lithium perchlorate, and lithium hexafluoroarsenate.Although the anode, cathode, and electrolyte layers may all be of solidpolymer material, when making a lithium polymer battery, it is preferredto have a layer of lithium metal as an anode.

Laminate structures further include electrochromic devices wherein anelectrolyte is sandwiched between electrochromic oxide layers.Conductive layers are placed on the electrochromic oxide layers forconnection to an electrical power source. Additional structural orprotective layers may be added to enclose an electro- chromic assembly.

Other polymers having added compounds, including but not limited toconductive powders and dyes, may be made by the present invention.

Presently, mass production of polymer and metal laminate structures usedfor electronic devices, and especially batteries, relies upon assemblingpreformed layers of polymer with a thin metal foil. Polymer layers areformed in production quantities by depositing a thin layer of a monomeronto a moving substrate that carries the monomer layer while and untilit is cured. Many means for forming polymer layers are available,including but not limited to physical or mechanical liquid-monomerspreading spreading apparati; for example, roll coaters, gravure rollcoaters, wire wound rods, doctor blades, and slotted dies, as well asmeans for evaporation and deposition of a monomer vapor, for examplepolymer multilayer deposition. In any means having a moving substrate,the substrate has a velocity different from a nozzle or bath thatdeposits the liquid monomer onto the substrate. Hence, the term "movingsubstrate" as used herein excludes a situation wherein there is norelative motion or velocity differential between substrate andliquid-monomer dispensing means.

The polymer multilayer deposition technique is distinct fromliquid-monomer spreading techniques because polymer multilayerdeposition requires flash evaporation of the monomer. First, a monomeris atomized into a heated chamber that is under vacuum. Within theheated chamber the monomer droplets are evaporated, then exit the heatedchamber, and monomer vapor condenses upon a substrate and issubsequently cured.

Curing may be done by any means including but not limited to heat,infrared light, ultraviolet light, electron beam, and other radiation.

When fabricating a battery, several techniques are used to combine athin metal layer with a conductive polymer layer. One technique ofbattery fabrication is to combine a metal foil with a conductive polymerlayer by press bonding a metal foil layer to a solid conductive polymerlayer. Another technique is to spread uncured conductive monomer onto ametal foil and subsequently cure the conductive monomer to form a solidconductive polymer layer. Use of metal foil, especially lithium metalfoil, results in minimum metal thicknesses of from about 1.5 mils (40micrometers) to about 2 mils (50 micrometers).

Other battery fabrication techniques include making a thin metal layerby sputtering, plating, or vacuum depositing metal onto a metalsubstrate. A conductive polymer is then placed in contact with themetal. Either solid conductive polymer or uncured conductive monomer maybe brought into contact with the metal to form the battery. Polymerlaminate structures, including but not limited to batteries, are made bya procedure wherein individual layers are sequentially and separatelyformed then combined.

The performance and lifetime of polymer/polymer and polymer/metallaminate structures depend upon the quality of bonding between laminatelayers. Bonding quality is affected by the presence of small, evenmicroscale, areas of non-bonding at an interface between laminatelayers. The bonding is especially critical between dissimilar layers;for example, polymer and metal layers. In batteries, reduced bondquality between polymer and lithium metal layers results in greaterinternal resistance of a battery produced with the laminate material andpotential for "hot spots" upon recharging. In any structure, anotherproblem with bonding dissimilar materials is chemical interactionbetween the materials. Areas of non-bonding can enhance chemicalinteraction because they may contain non-inert species or providedifferent surface characteristics at a boundary between bonded andunbonded areas.

Bonding between layers is therefore of great importance and is enhancedby several means, including but not limited to mechanical presses, andapplication of a second layer as a liquid with subsequent solidificationupon a first solid layer at atmospheric pressure. The difficulty withthese methods is that the low cost assembly of pressing or liquidapplication leads to low quality bonding as identified in U.S. Pat. No.4,098,965, issued Jul. 4, 1976, to Kinsman, column 1, lines 47-50,wherein he states "[g]ases usually air, [that] are included in the voidregions of the battery during assembly . . . ".

Likewise, bonding between layers within electrochromic devices and otherlaminate structures is directly related to the performance of thedevices.

It is of great interest to those skilled in the art, then, to makebatteries and other laminate structures having high bond quality whilemaking them in a cost effective manner.

SUMMARY OF THE INVENTION

The present invention is the formation of solid polymer layers undervacuum. More specifically, according to a first aspect of the presentinvention, "standard" polymer-layer making equipment that is generallyused in an atmospheric environment is placed in a vacuum, with anadditional step of degassing the monomer material prior to injectioninto the vacuum. Additionally, other layers of polymer or metal or oxidemay be vacuum deposited onto solid polymer layers.

Advantages of forming polymer layers in a vacuum include use of less tono photoinitiator for curing, faster curing, and fewer impurities in thepolymer. Further advantages are improvement in material properties,including no trapped gas, resulting in greater density and reducedmonomer wetting angle that facilitates spreading of the monomer andprovides a smoother finished surface.

According to a second aspect of the invention, fabrication of laminatestructures are carried out nearly simultaneously within a single vacuumchamber.

The subject matter of the present invention is particularly pointed outand distinctly claimed in the concluding portion of this specification.However, both the organization and method of operation, together withfurther advantages and objects thereof, may best be understood byreference to the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a preferred emodiment of the presentinvention.

FIG. 2 is a partial cross section including a mechanical liquid monomerspreading apparatus.

FIG. 3 is a cross section having additional means for depositingdegassed liquid monomer.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The method of the present invention is making a solid polymer layer byutilizing two known steps in combination with two additional steps thathad not been combined prior to the present invention. The known steps ofdepositing a thin layer of liquid monomer onto a moving substratefollowed by curing said monomer and forming the solid polymer layer, arecombined with the steps of (a) placing the moving substrate into avacuum chamber, and (b) degassing the monomer prior to depositing thedegassed monomer onto the moving substrate in the vacuum chamber.

The substrate may be a temporary substrate from which the solid polymerlayer product is removed after curing, or the substrate may be apermanent substrate forming part of the final product. The permanentsubstrate can be as simple as a base polymer layer having a metalizedsurface, for example, a solar reflector. The present invention may beused to place a protective coating upon the metallic surface. Thepermanent substrate may be as complex as a many-layered monolithicelectronic device, for example, a capacitor in which the presentinvention may be used to place multiple polymer and metal layers toconstruct the device.

According to the present invention, any polymer-layer making method donein air or other atmosphere may be adapted to be carried out in a vacuum.

The apparatus of the present invention is a combination of known meanswith additional means that had not been combined prior to the presentinvention. Apparatus for making a solid polymer layer includes a movingsubstrate together with means for depositing a thin layer of liquidmonomer onto the moving substrate, followed by means for curing theliquid monomer and forming the solid polymer. These means are combinedwith (a) means for creating a vacuum about the moving substrate, and (b)means for degassing the liquid monomer prior to depositing the degassedliquid monomer onto the moving substrate in the vacuum.

For making a polymer/metal laminate structure, the metal is vacuumdeposited onto a cured solid polymer layer. Alternatively, the metal maybe vacuum deposited onto a substrate, then liquid monomer deposited andspread under vacuum onto the metal surface. Any vacuum depositiontechnique may be used, but electron beam evaporation is preferred,especially for vacuum deposition of lithium metal. While any metalthickness is achievable with vacuum deposition techniques, a practicalrange of thickness is from about 10 angstroms to about 0.4 mils (10micrometers). For making a lithium polymer battery, it is preferred thatthe cathode and electrolyte are conductive polymer layers and that theanode is lithium metal.

For making additional polymer/oxide laminate structure, the oxide isvacuum deposited onto a cured solid polymer layer. Any oxide vacuumdeposition technique may be used, but reactive sputtering is preferredto maintain composition of the oxide layer and improved control overfilm structure.

Creating a vacuum about a moving substrate may be done in many ways,including housing an entire solid polymer-making apparatus in a vacuumchamber. Alternatively, a vacuum chamber may contain a moving substrateand a nozzle or coating head penetrating a wall of the vacuum chamberfor admitting liquid monomer material.

Degassing of the liquid monomer may be carried out in any way, but it ispreferred that the monomer be degassed by stirring it in a sealed vesseland removing residual gas with a vacuum pump. The vacuum pump draws avacuum of a pressure that removes a sufficient quantity of gas from theliquid monomer to permit smooth flow of the liquid monomer through anozzle into the vacuum chamber with reduced entrained gas expansion,thereby preventing intermittent nozzle discharge, or spitting. Theamount of entrained gas must also be sufficiently low to result in anacceptable quality polymer. Acceptable quality includes but is notlimited to the final polymer being free of void spaces and exhibiting asmooth surface.

The vacuum chamber may admit several liquid-monomer and other materialinlets for permitting multiple monomer/polymer layers, curing means, aswell as metal and/or oxide vacuum deposition means. With a multipleinlet vacuum chamber, laminate structures are made in one pass throughthe chamber. For example, a polymer layer may be cured, then a secondmetallic or oxide layer deposited, and a subsequent polymer layercovering the second surface put in place, all within the vacuum chamber.Multiple passes of a product through the vacuum chamber can developstacks of layered sets.

By placing liquid monomer spreading and vapor deposition of metal and/oroxide layer in the same vacuum chamber, the substrate velocity may beadjusted to accommodate both processes. Additionally, the flow ofmaterial through a nozzle may be adjusted to accommodate both processes.Similarly, vacuum pressure is set low enough to permit metal and/oroxide deposition.

A lithium polymer battery requires a minimum of three layers, anode(lithium metal) electrolyte polymer, and cathode polymer, respectively.Additional layers include a cathode current collector metal layer, andan anode current collector metal layer. The metal layers can be of anymetal or metal alloy but are preferably metals or alloys that arechemically compatible and highly electrically conductive, for examplegold, silver and copper. Moreover, first and second polymer insulatinglayers may be deposited onto the current collectors to form a cell.Cells may be stacked with or without intervening polymer insulatingmaterial.

Thus, a method of making a lithium polymer battery, according to thepresent invention has a minimum of six steps. The first three steps areequipment arrangement steps of (a) placing a moving substrate into avacuum chamber, (b) placing a mechanical liquid-monomer spreadingapparatus into the vacuum chamber, and (c) degassing a liquid monomercathode material. The next three steps are material deposition steps of(d) depositing a thin layer of the liquid monomer cathode material ontothe moving substrate, (e) curing the monomer cathode material andforming a solid cathode polymer, and (f) depositing and curing a thinlayer of monomer electrolyte material onto said cathode, forming a solidpolymer electrolyte with subsequent deposition of lithium metal ontosaid electrolyte, forming an anode.

For particular applications requiring current collectors and protectiveinsulating layers, two steps may precede the material deposition steps.Specifically, the additional steps of (g) depositing a first monomerinsu- lating material layer onto the moving substrate and curing thefirst monomer insulating material layer in advance of step (d)deposition of monomer cathode, and (h) depositing a cathode currentcollector metal onto the cured insulating material in advance of step(d) deposition of monomer cathode. Additionally, two steps may followthe material deposition steps, vis the steps of (i) depositing an anodecurrent collector onto the anode, and (j) depositing a second monomerinsulating layer onto the anode current collector and curing the secondmonomer insulating layer.

Electrochromic devices are similar to lithium polymer batteries in theaspect of an electrolyte layer combined with conductive layers. However,the specific layers are distinct so that the method of makingelectrochromic devices according to the present invention has the sameequipment arrangement steps of (a) placing a moving substrate into avacuum chamber, (b) placing a mechanical liquid-monomer spreadingapparatus into the vacuum chamber, and (c) degassing a liquid monomerelectrolyte material. However, the material deposition steps are (d)depositing a first conductive oxide layer onto the moving substrate, (e)depositing a first electrochromic oxide layer onto the first conductiveoxide layer, (f) depositing the liquid monomer electrolyte material ontothe first electrochromic oxide layer, (g) curing the liquid monomerelectrolyte to a solid polymer electrolyte, (h) depositing a secondelectrochromic oxide layer onto the solid polymer electrolyte, and (i)depositing a second conductive oxide layer onto the secondelectrochromic oxide layer.

Any conductive oxide layer material may be used, but preferredconductive oxide materials include, for example indium oxide, indium-tinoxide, tin oxide, and zinc oxide. Indium oxides are preferred.Electrochromic oxide materials include but are not limited to tungstenoxides, iridium oxides, and vanadium oxides.

While a preferred embodiment of the present invention has been shown anddescribed, it will be apparent to those skilled in the art that manychanges and modifications may be made without departing from theinvention in its broader aspects. The appended claims are thereforeintended to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

I claim:
 1. An apparatus for depositing a liquid monomer as a layer,comprising:(a) a moving substrate, (b) a vacuum chamber placed aboutsaid moving substrate, (c) means for degassing the liquid monomer, and(d) means for depositing a first layer including a nozzle for flowingthe degassed liquid monomer onto said moving substrate within the vacuumchamber.
 2. The apparatus as recited in claim 1, furthercomprising:additional means for vacuum depositing metal or fordepositing oxide onto said first layer, and a means for depositingfurther layers of degassed liquid monomer onto said vacuum depositedmetal or oxide, together with means for curing the degassed liquidmonomer layers.
 3. The apparatus as recited in claim 1, furthercomprising a mechanical liquid monomer spreading apparatus within thevacuum chamber.
 4. The apparatus as recited in claim 3 wherein saidmechanical liquid monomer spreading apparatus is selected from the groupof roll coaters, wire wound rods, doctor blade coaters, and slotted diecoaters.
 5. The apparatus as recited in claim 1, furthercomprising:means for curing, within the vacuum chamber, said liquidmonomer and forming a first solid polymer layer.
 6. The apparatus asrecited in claim 1, further comprising:additional means for vacuumdepositing a metal or oxide layer onto said first layer within thevacuum chamber.
 7. An apparatus for depositing a liquid monomer as alayer, comprising:(a) a moving substrate, (b) a vacuum chamber placedabout said moving substrate, (c) means for degassing the liquid monomer,(d) means for depositing a first layer of degassed liquid monomer ontosaid moving substrate within the vacuum chamber, and (e) a mechanicalliquid monomer spreading apparatus within said vacuum chamber forspreading deposited degassed liquid monomer on said moving substrate. 8.The apparatus as recited in claim 7, wherein said mechanical liquidmonomer spreading apparatus is selected from the group of roll coaters,wire would rods, doctor blade coaters, and slotted die coaters.
 9. Theapparatus as recited in claim 7, further comprising:additional means forvacuum depositing a metal or oxide layer onto said first layer withinthe vacuum chamber.
 10. The apparatus as recited in claim 9, furthercomprising:means for depositing further layers of degassed liquidmonomer onto said vacuum deposited metal or oxide, together with meansfor curing the degassed liquid monomer layers.
 11. An apparatus fordepositing a liquid monomer as a layer, comprising:(a) a movingsubstrate, (b) a vacuum chamber placed about said moving substrate, (c)means for degassing the liquid monomer, (d) means for depositing a firstlayer including a nozzle for flowing the degassed liquid monomer ontosaid moving substrate within the vacuum chamber, and (e) a means forvacuum depositing a metal or oxide layer onto said monomer layer. 12.The apparatus as recited in claim 11, further comprising a mechanicalliquid monomer spreading apparatus within the vacuum chamber.
 13. Theapparatus as recited in claim 12, wherein said mechanical liquid monomerspreading apparatus is selected from the group of roll coaters, wirewound rods, doctor blade coaters, and slotted die coaters.
 14. Theapparatus as recited in claim 11, further comprising:means fordepositing further layers of degassed liquid monomer onto said vacuumdeposited metal or oxide, together with means for curing the degassedliquid monomer layers.